For the use of known endoprostheses for hip joints there is a principal alternative to secure the femoral portion in the femoral canal either with or without bone cement. The use of bone cement enables an intimate and secure connection between the shank and the bone. However, the danger encounters that so-called micro motions lead to a loosening of the shank in the bone cement which may cause a malfunction of the endoprosthesis. A surgical reoperation then is necessary. However, it requires considerable efforts to remove femoral portions implanted with bone cement.
With cementless shanks it is attempted to achieve an effective power transfer from the shank to the bone. For this, it is prerequisite that the shank is held in the bone canal under considerable tension. The removal of such a shank is much more simply than a shank implanted with aid of bone cement. However, a cementless shaft effects a higher load of the bone so that distortions of the bone may occur during the implantation operation. In order to achieve an intimate contact between a cementlessly implanted shank and the bone, it is known to provide the shank with surface irregularities, indentations or the like or to give the surface a predetermined geometric structure. The bone tissue is to grow into the indentations or irregularities after implantation and to improve the fixation of the shank or the load transfer, respectively.
It is also known to improve the ingrowth of the prosthesis shank in that the spaces between the shank and the intermedullary canal are filling with spongy material. Normally, body-own spongy material is used which is removed for example by the surgeon from the hip bone.
From the German Gebrauchsmuster DE-Gm 87 12 607, a femoral portion has become known having a stem formed as hollow body including a plurality of openings connecting the hollow space within the stem with the outer surface thereof. The openings are preferably formed at the front and the dorsal side and can have various configurations. The hollow stem has the advantage that it can be filled with body-own autologeous or heterologeous spongy material enabling a genuine bony ingrowth of the prosthesis in the femur by a genuine bony connection so that a secure anchoring can be achieved without deterioration over a longer period. With these prostheses, the problem arises that the spongy material has to be inserted through the lateral openings which is somewhat difficult for the surgeon. In particular, it is difficult to charge the shaft such that the shaft accommodates a uniformly distributed and compressed mass.
The object of the invention is to provide a femoral portion of a hip joint prosthesis which can be implanted without bone cement, however, enables an intimate connection with or a genuine ingrowth of the adjacent bone portions, respectively.
The object of the invention is to design an effective configuration for the stem of a hip joint prosthesis by which the charging with spongy material is facilitated.
This object is attained by the device of the invention.